In the present study, we investigate to take more evidence concerned with learning through argument with teacher-led scaffolding in national language classes in a Japanese high school. We focused on the functional cooperation between students’ discussion-based learning and teacher-led scaffoldings. The second grade of 10 students participated in the national language class organized as one of advanced courses of extra-curriculum for preparation of the university entrance examination. Three or four students were brought together in a group and required to take perspectives of examination designer to create university entrance examination reading question. With Resnick et al.(1993)’s developed graphic coding system applied, we made comparative and pseudo-experimental design to investigate the effect of timing of teacher-led scaffolding (early-, mid-, late-period) on the students’ collaborative learning. Main results showed that there seemed to be better timing (during mid- to late-period) of the arugument when teacher-led scaffolding could cooperate with students’ collaborative discussion for the creation of reading question with a model answer based on the robust accountability of logical reasoning they shared.